Photodetection system

ABSTRACT

An optical scan device includes an optical waveguide array, including a plurality of optical waveguides each of which propagates light along a first direction, that emits a light beam, the plurality of optical waveguides being arranged in a second direction that intersects the first direction, a phase shifter array including a plurality of phase shifters connected separately to each of the plurality of optical waveguides, a control circuit that controls a phase shift amount of each of the plurality of phase shifters and/or inputting of light to each of the plurality of phase shifters and thereby controls a direction and shape of the light beam that is emitted from the optical waveguide array, a photodetector that detects the light beam reflected by a physical object, and a signal processing circuit that generates distance distribution data on the basis of output from the photodetector.

BACKGROUND 1. Technical Field

The present disclosure relates to a photodetection system.

2. Description of the Related Art

There have conventionally been proposed various types of device that arecapable of scanning space with light.

International Publication No. 2013/168266 and U.S. Patent ApplicationPublication No. 2016/0245903 each disclose a configuration in which anoptical scan can be performed with a mirror-rotating driving apparatus.

Japanese Unexamined Patent Application Publication (Translation of PCTApplication) No. 2016-508235 discloses an optical phased array having aplurality of two-dimensionally arrayed nanophotonic antenna elements.Each antenna element is optically coupled to a variable optical delayline (i.e. a phase shifter). In this optical phased array, a coherentlight beam is guided to each antenna element by an optical waveguide,and the phase of the light beam is shifted by the phase shifter. Thismakes it possible to vary the amplitude distribution of a far-fieldradiating pattern.

Japanese Unexamined Patent Application Publication No. 2013-16591discloses an optical deflection element including: an optical waveguideincluding an optical waveguide layer through the inside of which lightis guided and first distributed Bragg reflectors formed on upper andlower surfaces, respectively, of the optical waveguide layer; a lightentrance through which light enters the optical waveguide, and a lightexit formed on a surface of the optical waveguide to let out lighthaving entered through the light entrance and being guided through theinside of the optical waveguide.

SUMMARY

One non-limiting and exemplary embodiment provides a photodetectionsystem that performs a distance measurement while actively changing thedirection and shape of a light beam.

In one general aspect, the techniques disclosed here feature aphotodetection system including: an optical waveguide array, including aplurality of optical waveguides each of which propagates light along afirst direction, that emits a light beam, the plurality of opticalwaveguides being arranged in a second direction that intersects thefirst direction; a phase shifter array including a plurality of phaseshifters connected separately to each of the plurality of opticalwaveguides; a control circuit that controls a phase shift amount of eachof the plurality of phase shifters and/or inputting of light to each ofthe plurality of phase shifters and thereby controls a direction andshape of the light beam that is emitted from the optical waveguidearray; a photodetector that detects the light beam reflected by aphysical object; and a signal processing circuit that generates distancedistribution data on the basis of output from the photodetector.

It should be noted that general or specific embodiments may beimplemented as a device, a system, a method, or any selectivecombination thereof.

An aspect of the present disclosure makes it possible to perform adistance measurement while actively changing the direction and shape ofa light beam.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing a configuration of anoptical scan device according to an exemplary embodiment of the presentdisclosure;

FIG. 2 is a diagram schematically showing an example of a cross-sectionstructure of one optical waveguide element and an example of propagatinglight;

FIG. 3A is a diagram showing a cross-section of an optical waveguidearray that emits light in a direction perpendicular to an exit face ofthe optical waveguide array;

FIG. 3B is a diagram showing a cross-section of an optical waveguidearray that emits light in a direction different from a directionperpendicular to an exit face of the optical waveguide array;

FIG. 4 is a perspective view schematically showing an optical waveguidearray in a three-dimensional space;

FIG. 5 is a schematic view of an optical waveguide array and a phaseshifter array as seen from a direction (Z direction) normal to a lightexit face;

FIG. 6A is a diagram schematically showing an example of an optical scandevice according to the present embodiment and an example of thedirection of a light beam that is emitted from an optical waveguidearray;

FIG. 6B is a diagram schematically showing an example of the opticalscan device according to the present embodiment and an example of thedirection of the light beam that is emitted from the optical waveguidearray;

FIG. 7 is a diagram schematically showing an example of the optical scandevice according to the present embodiment and an example of thedirection of the light beam that is emitted from the optical waveguidearray;

FIG. 8A is a diagram schematically showing a modification of the opticalscan device shown in FIG. 7;

FIG. 8B is a diagram schematically showing a modification of the opticalscan device shown in FIG. 7;

FIG. 9 is a diagram schematically showing an example of the optical scandevice according to the present embodiment and an example of thedirection of the light beam that is emitted from the optical waveguidearray;

FIG. 10A is a diagram schematically showing a modification of theoptical scan device shown in FIG. 9;

FIG. 10B is a diagram schematically showing a modification of theoptical scan device shown in FIG. 9;

FIG. 10C is a diagram schematically showing a modification of theoptical scan device shown in FIG. 9;

FIG. 11 is a diagram showing a relationship between an angle and a lightintensity distribution when a second shift amount is zero;

FIG. 12A is a diagram showing a relationship between the angle and thelight intensity distribution when the second shift amount is not zero;

FIG. 12B is a diagram showing a relationship between the angle and thelight intensity distribution when the second shift amount is not zero;

FIG. 13 is a diagram showing a relationship between the angle and thelight intensity distribution when the second shift amount is not zero;

FIG. 14A is a diagram schematically showing an optical waveguideaccording to the present embodiment;

FIG. 14B is a diagram showing a relationship between the refractiveindex of an optical waveguide layer and the angle of emission of lightthat is emitted from the optical waveguide;

FIG. 15A is a diagram schematically showing an example of the shape of alight beam that is emitted from the optical waveguide array of theoptical scan device;

FIG. 15B is a diagram schematically showing an example of the shape of alight beam that is emitted from the optical waveguide array of theoptical scan device;

FIG. 15C is a diagram schematically showing an example of the shape of alight beam that is emitted from the optical waveguide array of theoptical scan device;

FIG. 16 is a diagram schematically showing examples of light beams thatare emitted from the optical scan device according to the presentembodiment and examples of distance images;

FIG. 17 is a diagram showing an example configuration of an optical scandevice in which elements such as an optical divider, an opticalwaveguide array, a phase shifter array, and a light source areintegrated on a circuit board;

FIG. 18 is a schematic view showing how a two-dimensional scan is beingexecuted by irradiating a distant place with a light beam such as alaser from the optical scan device; and

FIG. 19 is a block diagram showing an example configuration of a LiDARsystem that is capable of generating a ranging image.

DETAILED DESCRIPTION

Prior to a description of embodiments of the present disclosure,underlying knowledge forming the basis of the present disclosure isdescribed.

The inventors found that a conventional optical scan device hasdifficulty in scanning space with light without making a complexapparatus configuration.

For example, the technology disclosed in International Publication No.2013/168266 requires a mirror-rotating driving apparatus. Thisundesirably makes a complex apparatus configuration that is not robustagainst vibration.

In the optical phased array described in Japanese Unexamined PatentApplication Publication (Translation of PCT Application) No.2016-508235, it is necessary to divide light into lights, introduce thelights into a plurality of column waveguide and a plurality of rowwaveguides, and guide the lights to the plurality of two-dimensionallyarrayed antenna elements. This results in very complex wiring of opticalwaveguides through which to guide the lights. This also makes itimpossible to attain a great two-dimensional scanning range.Furthermore, to two-dimensionally vary the amplitude distribution ofemitted light in a far field, it is necessary to connect phase shiftersseparately to each of the plurality of two-dimensionally arrayed antennaelements and attach phase-controlling wires to the phase shifters. Thiscauses the phases of lights falling on the plurality oftwo-dimensionally arrayed antenna elements to vary by a differentamount. This makes the elements very complex in configuration.

The inventors focused on the foregoing problems in the conventionaltechnologies and studied configurations to solve these problems. Theinventors found that the foregoing problems can be solved by using anoptical waveguide element having a pair of mirrors facing each other andan optical waveguide layer sandwiched between the mirrors. One of thepair of mirrors of the optical waveguide element has a higher lighttransmittance than the other and lets out a portion of light propagatingthrough the optical waveguide layer. As will be mentioned later, thedirection of light emitted (or the angle of emission) can be changed byadjusting the refractive index or thickness of the optical waveguidelayer or the wavelength of light that is inputted to the opticalwaveguide layer. More specifically, by changing the refractive index,the thickness, or the wavelength, a component constituting the wavenumber vector (wave vector) of the emitted light and acting in adirection along a lengthwise direction of the optical waveguide layercan be changed. This allows a one-dimensional scan to be achieved.

Furthermore, in a case where an array of a plurality of the opticalwaveguide elements is used, a two-dimensional scan can be achieved. Morespecifically, a direction in which lights going out from the pluralityof optical waveguide elements reinforce each other can be changed bygiving an appropriate phase difference to lights that are supplied tothe plurality of optical waveguide elements and adjusting the phasedifference. A change in phase difference brings about a change in acomponent constituting the wave number vector of the emitted light andacting in a direction that intersects the direction along the lengthwisedirection of the optical waveguide layer. This makes it possible toachieve a two-dimensional scan. Even in a case where a two-dimensionalscan is performed, it is not necessary to cause the refractive index orthickness of each of a plurality of the optical waveguide layers or thewavelength of light to vary by a different amount. That is, atwo-dimensional scan can be performed by giving an appropriate phasedifference to lights that are supplied to the plurality of opticalwaveguide layers and causing at least one of the refractive index ofeach of the plurality of optical waveguide layers, the thickness of eachof the plurality of optical waveguide layers, or the wavelength to varyby the same amount in synchronization. In this way, an embodiment of thepresent disclosure makes it possible to achieve an opticaltwo-dimensional scanning through a comparatively simple configuration.

The phrase “at least one of the refractive index, the thickness, or thewavelength” herein means at least one selected from the group consistingof the refractive index of an optical waveguide layer, the thickness ofan optical waveguide layer, and the wavelength of light that is inputtedto an optical waveguide layer. For a change in direction of emission oflight, any one of the refractive index, the thickness, and thewavelength may be controlled alone. Alternatively, the direction ofemission of light may be changed by controlling any two or all of thesethree. In each of the following embodiments, the wavelength of lightthat is inputted to the optical waveguide layer may be controlledinstead of or in addition to controlling the refractive index or thethickness.

The foregoing fundamental principles are similarly applicable to uses inwhich optical signals are received as well as uses in which light isemitted. The direction of light that can be received can beone-dimensionally changed by changing at least one of the refractiveindex, the thickness, or the wavelength. Furthermore, the direction oflight that can be received can be two-dimensionally changed by changinga phase difference of light through a plurality of phase shiftersconnected separately to each of a plurality of unidirectionally-arrayedoptical waveguide elements.

An optical scan device and an optical receiver device according to anembodiment of the present disclosure may be used, for example, as anantenna in a photodetection system such as a LiDAR (light detection andraging) system. The LiDAR system, which involves the use ofshort-wavelength electromagnetic waves (visible light, infraredradiation, or ultraviolet radiation), can detect a distance distributionof objects with higher resolution than a radar system that involves theuse of radio waves such as millimeter waves. Such a LiDAR system ismounted, for example, on a movable body such as an automobile, a UAV(unmanned aerial vehicle, i.e. a drone), or an AGV (automated guidedvehicle), and may be used as one of the crash avoidance technologies.The optical scan device and the optical receiver device are hereinsometimes collectively referred to as “optical device”. Further, adevice that is used in the optical scan device or the optical receiverdevice is sometimes referred to as “optical device”, too.

The phrase “shape of a light beam” herein means the “shape and/or spreadangle of a light beam”.

Example Configuration of Optical Scan Device

The following describes, as an example, a configuration of an opticalscan device that performs a two-dimensional scan. Note, however, that anunnecessarily detailed description may be omitted. For example, adetailed description of a matter that is already well known and arepeated description of substantially the same configuration may beomitted. This is intended to facilitate understanding of persons skilledin the art by avoiding making the following description unnecessarilyredundant. It should be noted that the inventors provide theaccompanying drawings and the following description for persons skilledin the art to fully understand the present disclosure and do not intendto limit the subject matter recited in the claims. In the followingdescription, identical or similar constituent elements are given thesame reference numerals.

In the present disclosure, the term “light” means electromagnetic wavesincluding ultraviolet radiation (ranging from approximately 10 nm toapproximately 400 nm in wavelength) and infrared radiation (ranging fromapproximately 700 nm to approximately 1 mm in wavelength) as well asvisible light (ranging approximately 400 nm to approximately 700 nm inwavelength). Ultraviolet radiation is herein sometimes referred to as“ultraviolet light”, and infrared radiation is herein sometimes referredto as “infrared light”.

In the present disclosure, an optical “scan” means changing thedirection of light. A “one-dimensional scan” means changing thedirection of light along a direction that intersects the direction. A“two-dimensional scan” means two-dimensionally changing the direction oflight along a plane that intersects the direction.

When it is said herein that two directions are “parallel” to each other,it not only means that they are strictly parallel to each other but alsoencompasses a configuration in which they form an angle of 15 s orsmaller. When it is said herein that two directions are “perpendicular”to each other, it does not mean that they are strictly perpendicular toeach other but encompasses a configuration in which they form an angleof 75 degrees or larger and 105 degrees or smaller.

FIG. 1 is a perspective view schematically showing a configuration of anoptical scan device 100 according to an exemplary embodiment of thepresent disclosure. The optical scan device 100 includes an opticalwaveguide array including a plurality of optical waveguide elements 10.Each of the plurality of optical waveguide elements 10 has a shapeextending in a first direction (in FIG. 1, an X direction). Theplurality of optical waveguide elements 10 are regularly arrayed in asecond direction (in FIG. 1, a Y direction) that intersects the firstdirection. The plurality of optical waveguide elements 10, whilepropagating light in the first direction, emit the light in a thirddirection D3 that intersects an imaginary plane parallel to the firstand second directions. Although, in the present embodiment, the firstdirection (X direction) and the second direction (Y direction) areorthogonal to each other, they do not need to be orthogonal to eachother. Although, in the present embodiment, the plurality of opticalwaveguide elements 10 are placed at equal spacings in the Y direction,they do not necessarily need to be arranged at equal spacings.

It should be noted that the orientation of a structure shown in adrawing of the present disclosure is set in view of understandability ofexplanation and is in no way intended to restrict the orientation inwhich an embodiment of the present disclosure is carried out inactuality. Further, the shape and size of the whole or a part of astructure shown in a drawing are not intended to restrict an actualshape and size.

Each of the plurality of optical waveguide elements 10 has first andsecond mirrors 30 and 40 (each hereinafter sometimes referred to simplyas “mirror”) facing each other and an optical waveguide layer 20 locatedbetween the mirror 30 and the mirror 40. Each of the mirrors 30 and 40has a specular surface, situated at the interface with the opticalwaveguide layer 20, that intersects the third direction D3. The mirror30, the mirror 40, and the optical waveguide layer 20 have shapesextending in the first direction (X direction).

A plurality of the first mirrors 30 of the plurality of opticalwaveguide elements 10 may be a plurality of portions of a mirror ofintegral construction. Further, a plurality of the second mirrors 40 ofthe plurality of optical waveguide elements 10 may be a plurality ofportions of a mirror of integral construction. Furthermore, a pluralityof the optical waveguide layers 20 of the plurality of optical waveguideelements 10 may be a plurality of portions of an optical waveguide layerof integral construction. A plurality of optical waveguides can beformed by at least (1) each first mirror 30 being constructed separatelyfrom another first mirror 30, (2) each second mirror 40 beingconstructed separately from another second mirror 40, or (3) eachoptical waveguide layer 20 being constructed separately from anotheroptical waveguide layer 20. The phrase “being constructed separately”encompasses not only physically providing space but also separatingfirst mirrors 30, second mirrors 40, or optical waveguide layers 20 fromeach other by placing a material of a different refractive index betweenthem.

The specular surface of the first mirror 30 and the specular surface ofthe second mirror 40 face each other substantially in a parallelfashion. Of the two mirrors 30 and 40, at least the first mirror 30 hasthe property of transmitting a portion of light propagating through theoptical waveguide layer 30. In other words, the first mirror 30 has ahigher light transmittance against the light than the second mirror 40.For this reason, a portion of light propagating through the opticalwaveguide layer 20 is emitted outward from the first mirror 30. Suchmirrors 30 and 40 may for example be multilayer mirrors that are formedby multilayer films of dielectrics (sometimes referred to as “multilayerreflective films”).

An optical two-dimensional scan can be achieved by controlling thephases of lights that are inputted to the respective optical waveguideelements 10 and, furthermore, causing the refractive indices orthicknesses of the optical waveguide layers 20 of these opticalwaveguide elements 10 or the wavelengths of lights that are inputted tothe optical waveguide layers 20 to simultaneously change insynchronization.

In order to achieve such a two-dimensional scan, the inventors conductedan analysis on the principle of operation of an optical waveguideelement 10. As a result of their analysis, the inventors succeeded inachieving an optical two-dimensional scan by driving a plurality ofoptical waveguide elements 10 in synchronization.

As shown in FIG. 1, inputting light to each optical waveguide element 10causes light to exit the optical waveguide element 10 through an exitsurface of the optical waveguide element 10. The exit face is located onthe side opposite to the specular surface of the first mirror 30. Thedirection D3 of the emitted light depends on the refractive index andthickness of the optical waveguide layer and the wavelength of light. Inthe present embodiment, at least one of the refractive index of eachoptical waveguide layer, the thickness of each optical waveguide layer,or the wavelength is controlled in synchronization so that lights thatare emitted separately from each optical waveguide element 10 areoriented in substantially the same direction. This makes it possible tochange X-direction components of the wave number vectors of lights thatare emitted from the plurality of optical waveguide elements 10. Inother words, this makes it possible to change the direction D3 of theemitted light along a direction 101 shown in FIG. 1.

Furthermore, since the lights that are emitted from the plurality ofoptical waveguide elements 10 are oriented in the same direction, theemitted lights interfere with one another. By controlling the phases ofthe lights that are emitted from the respective optical waveguideelements 10, a direction in which the lights reinforce one another byinterference can be changed. For example, in a case where a plurality ofoptical waveguide elements 10 of the same size are placed at equalspacings in the Y direction, lights differing in phase by a constantamount from one another are inputted to the plurality of opticalwaveguide elements 10. By changing the phase differences, Y-directioncomponents of the wave number vectors of the emitted lights can bechanged. In other words, by varying phase differences among lights thatare introduced into the plurality of optical waveguide elements 10, thedirection D3, in which the emitted lights reinforce one another byinterference, can be changed along a direction 102 shown in FIG. 1. Thismakes it possible to achieve an optical two-dimensional scan.

The following describes the principle of operation of the optical scandevice 100.

Principle of Operation of Optical Waveguide Element

FIG. 2 is a diagram schematically showing an example of a cross-sectionstructure of one optical waveguide element 10 and an example ofpropagating light. With a Z direction being a direction perpendicular ofthe X and Y directions shown in FIG. 1, FIG. 2 schematically shows across-section parallel to an XZ plane of the optical waveguide element10. The optical waveguide element 10 is configured such that the pair ofmirrors 30 and 40 are disposed so as to hold the optical waveguide layer20 therebetween. Light 22 introduced into the optical waveguide layer 20through one end of the optical waveguide layer 20 in the X directionpropagates through the inside of the optical waveguide layer 20 whilebeing repeatedly reflected by the first mirror 30 provided on an uppersurface (in FIG. 2, the upper side) of the optical waveguide layer 20and the second mirror 40 provided on a lower surface (in FIG. 2, thelower side) of the optical waveguide layer 20. The light transmittanceof the first mirror 30 is higher than the light transmittance of thesecond mirror 40. For this reason, a portion of the light can beoutputted mainly from the first mirror 30.

In the case of an optical waveguide such as an ordinary optical fiber,light propagates along the optical waveguide while repeating totalreflection. On the other hand, in the case of an optical waveguideelement 10 according to the present embodiment, light propagates whilebeing repeatedly reflected by the mirrors 30 and 40 disposed above andbelow, respectively, the optical waveguide layer 20. For this reason,there are no restrictions on angles of propagation of light. The term“angle of propagation of light” here means an angle of incidence on theinterface between the mirror 30 or 40 and the optical waveguide layer20. Light falling on the mirror 30 or 40 at an angle that is closer tothe perpendicular can be propagated, too. That is, light falling on theinterface at an angle that is smaller than a critical angle of totalreflection can be propagated, too. This causes the group speed of lightin the direction of propagation of light to be much lower than the speedof light in free space. For this reason, the optical waveguide element10 has such a property that conditions for propagation of light varygreatly according to changes in the wavelength of light, the thicknessof the optical waveguide layer 20, and the refractive index of theoptical waveguide layer 20. Such an optical waveguide is referred to as“reflective optical waveguide” or “slow light optical waveguide”.

The angle of emission θ of light that is emitted into the air from theoptical waveguide element 10 is expressed by Formula (1) as follows:

$\begin{matrix}{{\sin\;\theta} = \sqrt{n_{w}^{2} - \left( \frac{m\;\lambda}{2\; d} \right)^{2}}} & (1)\end{matrix}$

As can be seen from Formula (1), the direction of emission of light canbe changed by changing any of the wavelength λ of light in the air, therefractive index n_(w) of the optical waveguide layer 20, and thethickness d of the optical waveguide layer 20.

For example, in a case where n_(w)=2, d=387 nm, λ=1550 nm, and m=1, theangle of emission is 0 degree. Changing the refractive index from thisstate to n_(w)=2.2 changes the angle of emission to approximately 66degrees. Meanwhile, changing the thickness to d=420 nm without changingthe refractive index changes the angle of emission to approximately 51degrees. Changing the wavelength to λ=1500 nm without changing therefractive index or the thickness changes the angle of emission toapproximately 30 degrees. In this way, the direction of emission oflight can be greatly changed by changing any of the wavelength λ oflight, the refractive index n_(w) of the optical waveguide layer 20, andthe thickness d of the optical waveguide layer 20.

Accordingly, the optical scan device 100 according to the embodiment ofthe present disclosure controls the direction of emission of light bycontrolling at least one of the wavelength λ of light that is inputtedto each of the optical waveguide layers 20, the refractive index n_(w)of each of the optical waveguide layers 20, or the thickness d of eachof the optical waveguide layers 20. The wavelength λ of light may bekept constant without being changed during operation. In that case, anoptical scan can be achieved through a simpler configuration. Thewavelength λ is not limited to a particular wavelength. For example, thewavelength λ may be included in a wavelength range of 400 nm to 1100 nm(from visible light to near-infrared light) within which high detectionsensitivity is attained by a common photodetector or image sensor thatdetects light by absorbing light through silicon (Si). In anotherexample, the wavelength λ may be included in a near-infrared wavelengthrange of 1260 nm to 1625 nm within which an optical fiber or a Sioptical waveguide has a comparatively small transmission loss. It shouldbe noted that these wavelength ranges are merely examples. A wavelengthrange of light that is used is not limited to a wavelength range ofvisible light or infrared light but may for example be a wavelengthrange of ultraviolet light.

In order to change the direction of emitted light, the optical scandevice 100 may include a first adjusting element that changes at leastone of the refractive index of the optical waveguide layer 20 of eachoptical waveguide element 10, the thickness of the optical waveguidelayer 20 of each optical waveguide element 10, or the wavelength.

As stated above, using an optical waveguide element 10 makes it possibleto greatly change the direction of emission of light by changing atleast one of the refractive index n_(w) of the optical waveguide layer20, the thickness d of the optical waveguide layer 20, or the wavelengthλ. This makes it possible to change, to a direction along the opticalwaveguide element 10, the angle of emission of light that is emittedfrom the mirror 30. By using at least one optical waveguide element 10,such a one-dimensional scan can be achieved.

In order to adjust the refractive index of at least a part of theoptical waveguide layer 20, the optical waveguide layer 20 may contain aliquid crystal material or an electro-optical material. The opticalwaveguide layer 20 may be sandwiched between a pair of electrodes. Byapplying the voltage to the pair of electrodes, the refractive index ofthe optical waveguide layer 20 can be changed.

In order to adjust the thickness of the optical waveguide layer 20, atleast one actuator may be connected, for example, to at least either thefirst mirror 30 or the second mirror 40. The thickness of the opticalwaveguide layer 20 can be changed by varying the distance between thefirst mirror 30 and the second mirror 40 through the at least oneactuator. When the optical waveguide layer 20 is formed from liquid, thethickness of the optical waveguide layer 20 may easily change.

Principle of Operation of Two-Dimensional Scan

In an optical waveguide array in which a plurality of optical waveguideelements 10 are unidirectionally arrayed, the interference of lightsthat are emitted from the respective optical waveguide elements 10brings about a change in direction of emission of light. By adjustingthe phases of lights that are supplied separately to each opticalwaveguide element 10, the direction of emission of light can be changed.The following describes the principles on which it is based.

FIG. 3A is a diagram showing a cross-section of an optical waveguidearray that emits light in a direction perpendicular to an exit face ofthe optical waveguide array. FIG. 3A also describes phase shift amountsof lights that propagate separately through each optical waveguideelement 10. Note here that the phase shift amounts are values based onthe phase of the light that propagates through the leftmost opticalwaveguide element 10. The optical waveguide array according to thepresent embodiment includes a plurality of optical waveguide elements 10arrayed at equal spacings. In FIG. 3A, the dotted circular arcs indicatethe wave fronts of lights that are emitted separately from each opticalwaveguide element 10. The straight line indicates a wave front that isformed by the interference of the lights. The arrow indicates thedirection of light that is emitted from the optical waveguide array(i.e. the direction of a wave number vector). In the example shown inFIG. 3A, lights propagating through the optical waveguide layers 20 ofeach separate optical waveguide element 10 are identical in phase to oneanother. In this case, the light is emitted in a direction (Z direction)perpendicular to both an array direction (Y direction) of the opticalwaveguide elements 10 and a direction (X direction) in which the opticalwaveguide layers 20 extend.

FIG. 3B is a diagram showing a cross-section of an optical waveguidearray that emits light in a direction different from a directionperpendicular to an exit face of the optical waveguide array. In theexample shown in FIG. 3B, lights propagating through the opticalwaveguide layers 20 of the plurality of optical waveguide elements 10differ in phase from one another by a constant amount (Δφ) in the arraydirection. In this case, the light is emitted in a direction differentfrom the Z direction. By varying Δφ, a Y-direction component of the wavenumber vector of the light can be changed. Assuming that p is thecenter-to-center distance between two adjacent optical waveguideelements 10, the angle of emission α₀ of light is expressed by Formula(2) as follows:

$\begin{matrix}{{\sin\;\alpha_{0}} = \frac{\Delta\phi\lambda}{2\;\pi\; p}} & (2)\end{matrix}$

When N is the number of optical waveguide elements 10, the spread angleΔα by which the angle of emission of light spreads is expressed byFormula (3) as follows:

$\begin{matrix}{{\Delta\alpha} = \frac{2\;\lambda}{{Np}\;\cos\;\alpha_{0}}} & (3)\end{matrix}$

Accordingly, a larger number of optical waveguide elements 10 can makethe spread angle Δα smaller, making it possible to achieve ahigh-definition optical scan even in a far field.

In the example shown in FIG. 2, the direction of emission of light isparallel to the XZ plane. That is, α₀=0°. In each of the examples shownin FIGS. 3A and 3B, the direction of light that is emitted from theoptical scan device 100 is parallel to a YZ plane. That is, θ=0°.However, in general, the direction of light that is emitted from theoptical scan device 100 is not parallel to the XZ plane or the YZ plane.That is, θ≠0° and α₀≠0°.

FIG. 4 is a perspective view schematically showing an optical waveguidearray in a three-dimensional space. The bold arrow shown in FIG. 4represents the direction of light that is emitted from the optical scandevice 100. θ is the angle formed by the direction of emission of lightand the YZ plane. θ satisfies Formula (1). α0 is the angle formed by thedirection of emission of light and the XZ plane. α₀ satisfies Formula(2).

Phase Control of Light That Is Introduced into Optical Waveguide Array

In order to control the phases of lights that are emitted from therespective optical waveguide elements 10, a phase shifter that changesthe phase of light may be provided, for example, at a stage prior to theintroduction of light into an optical waveguide element 10. The opticalscan device 100 according to the present embodiment includes a pluralityof phase shifters connected separately to each of the plurality ofoptical waveguide elements 10 and a second adjusting element thatadjusts the phases of lights that propagate separately through eachphase shifter. Each phase shifter includes an optical waveguide joinedeither directly or via another optical waveguide to the opticalwaveguide layer 20 of a corresponding one of the plurality of opticalwaveguide elements 10. The second adjusting element varies differencesin phase among lights propagating from the plurality of phase shiftersto the plurality of optical waveguide elements 10 and thereby changesthe direction (i.e. the third direction D3) of light that is emittedfrom the plurality of optical waveguide elements 10. As is the case withthe optical waveguide array, a plurality of arrayed phase shifters arehereinafter sometimes referred to as “phase shifter array”.

FIG. 5 is a schematic view of an optical waveguide array 10A and a phaseshifter array 80A as seen from a direction (Z direction) normal to alight exit face. In the example shown in FIG. 5, all phase shifters 80have the same propagation characteristics, and all optical waveguideelements 10 have the same propagation characteristics. The phase shifter80 and the optical waveguide elements 10 may be the same in length ormay be different in length. In a case where the phase shifters 80 areequal in length, the respective phase shift amounts can be adjusted, forexample, by a driving voltage. Further, by making a structure in whichthe lengths of the phase shifters 80 vary in equal steps, phase shiftscan be given in equal steps by the same driving voltage. Furthermore,this optical scan device 100 further includes an optical divider 90 thatdivides light into lights and supplies the lights to the plurality ofphase shifters 80, a first driving circuit 110 that drives each opticalwaveguide element 10, and a second driving circuit 210 that drives eachphase shifter 80. A two-dimensional scan can be achieved byindependently controlling the first driving circuit 110 and the seconddriving circuit 210, which are separately provided. In this example, thefirst driving circuit 110 functions as one element of the firstadjusting element, and the second driving circuit 210 functions as oneelement of the second adjusting element.

The first driving circuit 110 changes at least either the refractiveindex or thickness of the optical waveguide layer 20 of each opticalwaveguide element 10 and thereby changes the angle of light that isemitted from the optical waveguide layer 20. The second driving circuit210 changes the refractive index of the optical waveguide 20 a of eachphase shifter 80 and thereby changes the phase of light that propagatesthrough the inside of the optical waveguide 20 a. The optical divider 90may be constituted by an optical waveguide through which lightpropagates by total reflection or may be constituted by a reflectiveoptical waveguide that is similar to an optical waveguide element 10.

The lights divided by the optical divider 90 may be introduced into thephase shifters 80 after the phases of the lights have been controlled,respectively. This phase control may involve the use of, for example, apassive phase control structure based on an adjustment of the lengths ofoptical waveguides leading to the phase shifters 80. Alternatively, itis possible to use phase shifters that are similar in function to thephase shifters 80 and that can be controlled by electrical signals. Thephases may be adjusted by such a method prior to introduction into thephase shifters 80, for example, so that lights of equal phases aresupplied to all phase shifters 80. Such an adjustment makes it possibleto simplify the control of each phase shifter 80 by the second drivingcircuit 210.

An optical device that is similar in configuration to the aforementionedoptical scan device 100 can also be utilized as an optical receiverdevice. Details of the principle of operation of the optical device, amethod of operation of the optical device, and the like are disclosed inU.S. Patent Application Publication No. 2018/0224709, the disclosure ofwhich is hereby incorporated by reference herein in its entirety.

Control of Direction and Shape of Light Beam that is Emitted fromOptical Scan Device

The optical scan device 100 scans a physical object by changing thedirection of emission of light. A physical object that is present at ashort distance may be irradiated with a light beam of a large spot size.Meanwhile, a physical object that is present at a long distance isirradiated with a light beam of a small spot size. The intensity of alight beam reflected off and returning from a physical object at a longdistance may decrease due to scattering or attenuation. For this reason,a physical object at a long distance is irradiated with a light beam ofa small spot size so that the intensity of a light beam reflected offand returning from the physical object is increased. In this way, theoptical scan device 100 may scan a physical object by changing both thedirection and shape of a light beam.

A photodetection apparatus called “flash LiDAR” emits diffused laserlight and uses an image sensor to detect light reflected off andreturning from a physical object. This makes it possible to acquire adistance image of the physical object at once using a publicly-known TOF(time-of-flight) method. However, the flash LiDAR decreases in lightintensity due to the diffusion of the laser light. For this reason, itis not easy to accurately measure a distance to a physical object at along distance.

An optical device including a plurality of laser sources of differentspot sizes can accurately measure distances to physical objects at ashort distance and a long distance. The optical device irradiates aphysical object at a short distance with a light beam of a large spotsize and irradiates a physical object at a long distance with a lightbeam of a small spot size. The optical device uses many laser lightsources in order to accurately measure distances to physical objects ata short distance and a long distance. This results in increased cost.Further, the direction of light that is emitted from each laser sourceis fixed. This results in a narrow scanning range of physical objects.

U.S. Patent Application Publication No. 2016/0245903 discloses anoptical beam scan device that mechanically changes both the direction ofemission of a light beam and the spot size of a light beam. The deviceis configured such that the direction of emission of a light beamemitted from a light source is changed by a mechanically-movable mirrorreflecting the light beam. Furthermore, the device is configured suchthat two lenses are disposed in front of the light source and arrangedin the direction of emission of light. The spot size of the light beamis changed by an actuator varying the distance between the two lenses.Mechanical modulation such as that which is performed by the device isnot very high in modulation rate. Further, a mechanically-movable parteasily wears out and may lead to an increase in failure rate of thedevice.

Based on the foregoing study, the inventors conceived optical scandevices described in the following items.

A photodetection system according to a first item includes: an opticalwaveguide array, including a plurality of optical waveguides each ofwhich propagates light along a first direction, that emits a light beam,the plurality of optical waveguides being arranged in a second directionthat intersects the first direction; a phase shifter array including aplurality of phase shifters connected separately to each of theplurality of optical waveguides; a control circuit that controls a phaseshift amount of each of the plurality of phase shifters and/or inputtingof light to each of the plurality of phase shifters and thereby controlsa direction and shape of the light beam that is emitted from the opticalwaveguide array; a photodetector that detects the light beam reflectedby a physical object; and a signal processing circuit that generatesdistance distribution data on the basis of output from thephotodetector.

This photodetection system makes it possible to, by controlling thephase shift amount of each of the plurality of phase shifters and/or theinputting of the light to each of the plurality of phase shifters,change the direction and shape of the light beam that is emitted fromthe optical waveguide array. This makes it possible to generate distancedistribution data on physical objects that are present at a shortdistance, a middle distance, and a long distance.

A photodetection system according to a second item is directed to thephotodetection system according to the first item, wherein the controlcircuit is capable of independently changing a first control parameterthat controls the direction of the light beam and a second controlparameter that controls the shape of the light beam.

This photodetection system makes it possible to, by independentlychanging the first control parameter and the second control parameter,reduce the number of control signals that control the direction andshape of the light beam.

A photodetection system according to a third item is directed to thephotodetection system according to the second item, wherein the phaseshift amount of each of the plurality of phase shifters is a sum of afirst shift amount and a second shift amount, and the control circuitcontrols the direction of the light beam by controlling the firstcontrol shift amount of each of the plurality of phase shifters andcontrols the shape of the light beam by controlling the second shiftamount of each of the plurality of phase shifters.

This photodetection system brings about the same effect as thephotodetection system according to the second item.

A photodetection system according to a fourth item is directed to thephotodetection system according to the third item, wherein the seconddirection is perpendicular to the first direction, the plurality ofoptical waveguides are arranged at equal spacings in the seconddirection, the plurality of phase shifters are arranged as equalspacings in the second direction and connected directly to the pluralityof optical waveguides, and the control circuit determines the firstshift amount of each of the plurality of phase shifters so that thefirst shift amount varies by a constant amount in an order in which theplurality of phase shifters are arrayed in the second direction.

This photodetection system makes it possible to change, through theoperation of the control circuit, a component constituting the directionof the light beam and acting parallel to the second direction.

A photodetection system according to a fifth item is directed to thephotodetection system according to the third or fourth item, wherein thecontrol circuit adjusts the second shift amount of each of the pluralityof phase shifters and thereby causes the optical waveguide array to emita light beam having a predetermined spread angle.

This photodetection system makes it possible to control, through theoperation of the control circuit, the spread angle of the light beam inthe second direction.

A photodetection system according to a sixth item is directed to thephotodetection system according to the fifth item, wherein the controlcircuit determines the second shift amount of each of the plurality ofphase shifters on the basis of random numbers.

This photodetection system makes it possible to sufficiently widen theshape of the light beam in the second direction.

A photodetection system according to a seventh item is directed to thephotodetection system according to the first item, wherein the pluralityof phase shifters are constituted by a plurality of phase shifter groupsarranged in the second direction, each of the plurality of phase shiftergroups includes one or more phase shifters, and a difference in phaseshift amount between two phase shifters at a boundary between adjacentphase shifter groups is different from a difference in phase shiftamount between two adjacent phase shifters in one phase shifter group.

This photodetection system causes lights to be emitted in a plurality ofdirections from the optical waveguide array. The number of the pluralityof directions is equal to the number of phase shifter groups.

A photodetection system according to an eighth item is directed to thephotodetection system according to the second item, wherein the controlcircuit controls the direction of the light beam by controlling thephase shift amount of each of the plurality of phase shifters andcontrols the shape of the light beam by controlling the inputting of thelight to each of the plurality of phase shifters.

This photodetection system makes it possible to independently control,through the operation of the control circuit, a component constitutingthe direction of the light beam and acting parallel to the seconddirection and the shape of the light beam in the second direction.Control of the inputting of the light to each of the phase shifters canbe achieved, for example, by providing an optical switch at a branchpoint of an optical divider connected to the plurality of phaseshifters.

A photodetection system according to a ninth item is directed to thephotodetection system according to any of the first to eighth items,wherein each of the plurality of phase shifters includes an opticalwaveguide connected to a corresponding one of the plurality ofwaveguides, the optical waveguide is constituted by a material whoserefractive index changes when a voltage is applied, and the controlcircuit changes the phase shift amount by changing the refractive indexby applying the voltage to the optical waveguide of each of theplurality of phase shifters.

This photodetection system makes it possible to change the phase shiftamount by applying the voltage to each of the plurality of phaseshifters.

A photodetection system according to a tenth item is directed to thephotodetection system according to the ninth item, further including apair of electrodes directly or indirectly holding the optical waveguideof each of the plurality of phase shifters therebetween. The opticalwaveguide of each of the plurality of phase shifters contains a liquidcrystal material or an electro-optical material. The control circuitchanges the refractive index of the optical waveguide by applying thevoltage to the pair of electrodes.

This photodetection system brings about the same effect as thephotodetection system according to the ninth item.

A photodetection system according to an eleventh item is directed to thephotodetection system according to any of the first to tenth items,wherein each of the plurality of optical waveguides includes a firstmirror extending in the first direction, a second mirror facing thefirst mirror and extending in the first direction, and an opticalwaveguide layer, located between the first mirror and the second mirror,that propagates light along the first direction, a transmittance of thefirst mirror is higher than a transmittance of the second mirror, andthe light beam is emitted via the first mirror from the plurality ofoptical waveguides.

In this photodetection system, each of the plurality of opticalwaveguides is a reflective waveguide. This causes the light beam to beemitted in a direction that intersects a surface on which the opticalwaveguide array is placed.

A photodetection system according to a twelfth item is directed to thephotodetection system according to the eleventh item, further includingfirst and second electrodes directly or indirectly holding the opticalwaveguide layer therebetween. The optical waveguide layer of each of theplurality of optical waveguides is constituted by a material whoserefractive index changes when a voltage is applied. The first electrodeincludes a plurality of electrode sections arranged in the firstdirection. The control circuit controls voltages that are appliedbetween the plurality of electrode sections of the first electrode andthe second electrode and thereby changes the direction and shape of thelight beam that is emitted from the optical waveguide array.

This photodetection system causes the light beam to be emitted from eachof the plurality of portions of the optical waveguide layer that overlapthe plurality of electrode sections, respectively. This makes itpossible to change a component constituting the direction of the lightbeam that is emitted from the optical waveguide array and actingparallel to the first direction and the shape of the light beam in thefirst direction.

A photodetection system according to a thirteenth item is directed tothe photodetection system according to the twelfth item, wherein thevoltages that are applied to the plurality of electrode sections areeach a sum of a first voltage and a second voltage, and the controlcircuit controls the direction of the light beam by controlling thefirst voltage and controls the shape of the light beam by controllingthe second voltage.

This photodetection system makes it possible to independently change acomponent constituting the direction of the light beam that is emittedfrom the optical waveguide array and acting parallel to the firstdirection and the shape of the light beam in the first direction.

A photodetection system according to a fourteenth item is directed tothe photodetection system according to the twelfth or thirteenth item,wherein the material whose refractive index changes when a voltage isapplied is a liquid crystal material or an electro-optical material.

This photodetection system brings about the same effect as thephotodetection system according to the twelfth or thirteenth item.

A photodetection system according to a fifteenth item is directed to thephotodetection system according to any of the eleventh to thirteenthitems, wherein a spread angle in either one of the first or seconddirections of the light beam that is emitted from the optical waveguidearray is larger than a spread angle in the other one of the first orsecond directions of the light beam that is emitted from the opticalwaveguide array, and the control circuit controls the direction of thelight beam so that the light beam is passed in one of the first andsecond directions that is smaller in spread angle.

This photodetection system makes it possible to scan a predeterminedarea in its entirety by shifting, in a one-dimensional direction, alight beam emitted from the optical waveguide array.

A photodetection system according to a sixteenth item includes: anoptical scan device that is capable of controlling a direction and shapeof a light beam; an image sensor, having a plurality of pixels, thatdetects the light beams reflected by a physical object; and a signalprocessing circuit that generates distance distribution data on thebasis of output from the image sensor. The optical scan deviceirradiates, with the light beam having a first spread angle, a firstarea in a scene that the image sensor shoots and irradiates, with thelight beam having a second spread angle that is larger than the firstspread angle, a second area in the scene that is at a shorter distancethan the first area.

This photodetection system makes it possible to generate distancedistribution data on physical objects that are present at differentdistances.

Embodiment

FIGS. 6A and 6B are diagrams each schematically showing an example of anoptical scan device 100 according to the present embodiment and anexample of the direction of a light beam that is emitted from an opticalwaveguide array 10A. The drawing on the left side of the vertical dashedline is a drawing schematically showing an example of the optical scandevice 100 on an XY plane. The drawing on the right side of the verticaldashed line is a drawing schematically showing the direction in a YZplane of a light beam that is emitted from the optical waveguide array10A. The same applies to the following drawings. Optical waveguideelements 10 are hereinafter sometimes referred to simply as “opticalwaveguides 10”.

In each of the examples shown in FIGS. 6A and 6B, the optical scandevice 100 includes an optical waveguide array 10A, a phase shifterarray 80A, an optical divider 90, and a control circuit 500.

The optical waveguide array 10A includes a plurality of opticalwaveguides 10 each of which propagates light along the X direction. Theplurality of optical waveguides 10 are arranged in the Y direction andemit a light beam in a direction that intersects the XY plane. In eachof the examples shown in FIGS. 6A and 6B, the plurality of opticalwaveguides 10 are arranged in the Y direction, which is perpendicular tothe X direction.

The phase shifter array 80A includes a plurality of phase shifters 80connected separately to each of the plurality of optical waveguides 10.The plurality of phase shifters 80A are arranged at equal spacings inthe Y direction, which is perpendicular to the X direction, andconnected directly to the plurality of optical waveguides 10. Each ofthe plurality of phase shifters 80A includes an optical waveguideconnected to a corresponding one of the plurality of optical waveguides10. The optical waveguide is constituted by a material whose refractiveindex changes when a voltage is applied. In a case where the opticalwaveguide of each of the plurality of phase shifters 80 contains aliquid crystal material or an electro-optical material, the optical scandevice 100 further includes a pair of electrodes directly or indirectlyholding the optical waveguide of each of the plurality of phase shifters80 therebetween.

The liquid crystal material may for example be nematic liquid crystals.The molecular structure of a nematic liquid crystal is as follows:

R1-Ph1-R2-Ph2-R3

where R1 is any one member selected from the group consisting of anamino group, a carbonyl group, a carboxyl group, a cyano group, an aminegroup, a nitro group, a nitryl group, and an alkyl chain, R3 is any onemember selected from the group consisting of an amino group, a carbonylgroup, a carboxyl group, a cyano group, an amine group, a nitro group, anitryl group, and an alkyl chain, Ph1 is an aromatic group such as aphenyl group or a biphenyl group, Ph2 is an aromatic group such as aphenyl group or a biphenyl group, and R2 is any one member selected fromthe group consisting of a vinyl group, a carbonyl group, a carboxylgroup, a diazo group, and an azoxy group.

The liquid crystals are not limited to nematic liquid crystals. Forexample, smectic liquid crystals may be used. Among smectic liquidcrystals, the liquid crystals may for example be in a smectic C phase(SmC phase). Among smectic C phases (SmC phases), the smectic liquidcrystals may for example be in a chiral smectic phase (SmC* phase), i.e.ferroelectric liquid crystals each having a chiral center such asasymmetric carbon within a liquid crystal molecule.

The molecule structure of the SmC* phase is expressed as follows:

where R1 and R4 are each independently any one member selected from thegroup consisting of an amino group, a carbonyl group, a carboxyl group,a cyano group, an amine group, a nitro group, a nitryl group, and analkyl chain, Ph1 is an aromatic group such as a phenyl group or abiphenyl group, Ph2 is an aromatic group such as a phenyl group or abiphenyl group, R2 is any one member selected from the group consistingof a vinyl group, a carbonyl group, a carboxyl group, a diazo group, andan azoxy group, Ch* is a chiral center, which is typically carbon (C*),R3 is any one member selected from the group consisting of hydrogen, amethyl group, an amino group, a carbonyl group, a carboxyl group, acyano group, an amine group, a nitro group, a nitryl group, and an alkylchain, R5 is any one member selected from the group consisting ofhydrogen, a methyl group, an amino group, a carbonyl group, a carboxylgroup, a cyano group, an amine group, a nitro group, a nitryl group, andan alkyl chain, and R3, R4, and R5 are functional groups that aredifferent from one another.

The liquid crystal material may be a mixture of a plurality of liquidcrystal molecules that are different in composition from each other. Forexample, a mixture of nematic liquid crystal molecules and smecticliquid crystal molecules may be used as the material of the opticalwaveguide layer 20.

The electro-optical material may be any of the following compounds:

KDP (KH₂PO₄) crystal . . . For example, KDP, ADP (NH₄H₂PO₄), KDA(KH₂AsO₄), RDA (RbH₂PO₄), or ADA (NH₄H₂AsO₄)

Cubic system material . . . For example, KTN, BaTiO₃, SrTiO₃Pb₃,MgNb₂O₉, GaAs, CdTe, or InAs

Tetragonal system material . . . For example, LiNbO₃ or LiTaO₃

Zinc blende material . . . For example, ZnS, ZnSe, ZnTe, GaAs, or CuCl

Tungsten bronze material . . . KLiNbO₃, SrBaNb₂O₆, KSrNbO, BaNaNbO, orCa₂Nb₂O₇

The optical divider 90 includes one or more optical switches 90S at oneor more optical branch points. The optical divider 90 does not need toinclude optical switches 90S at all optical branch points. The opticalswitches 90S make it possible to switch between the inputting andblocking of light to each of the plurality of phase shifters 80.

The control circuit 500 controls a phase shift amount φ_(i) of each ofthe plurality of phase shifters 80 in accordance with a first controlsignal 500 a. The phase shift amount (pi represents a phase shift amountof the ith phase shifter as counted from the bottom. The control circuit500 changes the phase shift amount by changing the refractive index byapplying the voltage to the optical waveguide of each phase shifter 80.In a case where the optical waveguide of each of the plurality of phaseshifters 80 contains a liquid crystal material or an electro-opticalmaterial, the control circuit 500 can change the refractive index of theoptical waveguide of each of the phase shifters 80 by applying thevoltage to the pair of electrodes. The control circuit 500 determinesthe phase shift amount so that as shown in FIGS. 6A and 6B, the phaseshift amount φ_(i)=(i−1)Δφ varies by a constant amount Δφ in the orderin which the phase shifters 80 are arrayed. This makes it possible tocontrol a Y-direction component of the direction of the light beam thatis emitted from the optical waveguide array 10A.

The control circuit 500 controls the switching of the optical switches90S in accordance with a second control signal 500 b. As a result, inthe example shown in FIG. 6A, the control circuit 500 inputs lights tothe lower four phase shifters 80, and in the example shown in FIG. 6B,the control circuit 500 inputs lights to the lower two phase shifters80. The spread angle of the light beam is expressed by Formula (3),which has been mentioned before. That is, the larger the number N ofoptical waveguides 10 becomes, the smaller the spread angle of the lightbeam becomes. Accordingly, the spread angle of the light beam in theexample shown in FIG. 6A is smaller than the spread angle of the lightbeam in the example shown in FIG. 6B. In this way, the control circuit500 uses the optical switches 90S to control the inputting of the lightto each of the plurality of phase shifters 80. This makes it possible tocontrol the shape of the light beam that is emitted from the opticalwaveguide array 10A.

In each of the examples shown in FIGS. 6A and 6B, the optical switches90S are used as new constituent elements. Usable examples of the opticalswitches 90S include Mach-Zehnder interferometers. A Mach-Zehnderinterferometer manufactured with a high degree of processing accuracymakes it possible to make the proportion of light propagation of one ofthe two branches 100% and make the proportion of light propagation ofthe other branch 0% or to reduce a loss of light resulting frombranching. However, it is not easy to stably manufacture such aMach-Zehnder interferometer.

The following describes an optical scan device 100 that does not involvethe use of an optical switch 90S.

FIG. 7 is a diagram schematically showing an example of the optical scandevice 100 according to the present embodiment and an example of thedirection of the light beam that is emitted from the optical waveguidearray 10A.

In the example shown in FIG. 7, the optical scan device 100 includes anoptical waveguide array 10A, a phase shifter array 80A, an opticaldivider 90, and a control circuit 500. The optical waveguide array 10Aand the phase shifter array 80A in the example shown in FIG. 7 areidentical to the optical waveguide array 10A and the phase shifter array80A in each of the examples shown in FIGS. 6A and 6B.

In the example shown in FIG. 7, by controlling the phase shift amount ofeach of the plurality of phase shifters 80, the control circuit 500controls both the direction and shape of the light beam that is emittedfrom the optical waveguide array 10A. In the example shown in FIG. 7,the phase shift amount of the ith phase shifter 80 as counted from thebottom is the sum of a first shift amount φ_(i) and a second shiftamount V_(i).

The control circuit 500 controls the direction of the light beam bycontrolling the first shift amount (pi of the phase shifter 80 inaccordance with the first control signal 500 a. Specifically, thecontrol circuit 500 determines the phase shift amount so that as shownin FIG. 7, the phase shift amount φ_(i)=(i−1)Δφ varies by a constantamount Δφ in the order in which the phase shifters 80 are arrayed. Thismakes it possible to control a Y-direction component of the direction ofthe light beam that is emitted from the optical waveguide array 10A.

The control circuit 500 controls the shape of the light beam bycontrolling the second shift amount V_(i) of the phase shifter 80 inaccordance with the second control signal 500 b. The shape of a lightbeam in a far field is obtained by performing Fourier transformation ona space pattern of the intensity and phase of a light beam just emittedfrom the optical waveguide array 10A. Based on this principle, thecontrol circuit 500 can determine the second shift amount V_(i) of thephase shifter 80 according to the desired shape of a light beam in a farfield. For example, in sufficiently spreading the shape of a light beam,the control circuit 500 determines the second shift amount V_(i) of eachof the plurality of phase shifters 80 on the basis of random numbers.This randomizes the second shift amount V_(i).

As shown in FIG. 7, independently controlling the first shift amountφ_(i) and the second shift amount V_(i) in accordance with the firstcontrol signal 500 a and the second control signal 500 b, respectively,has the following advantage. In a case where the direction and shape ofa light beam is controlled in accordance with one control signal, thenumber of control signals that are stored in a memory (not illustrated)of the control circuit 500 is the product of the number of desireddirections of emission and the number of desired shapes. Meanwhile, in acase where the direction and shape of a light beam are independentlycontrolled in accordance with two control signals, the number of controlsignals that are stored in the memory (not illustrated) of the controlcircuit 500 is the sum of the number of desired directions of emissionand the number of desired shapes. Accordingly, independent control makesit possible to greatly reduce the number of data that represent controlsignals that are stored in the memory (not illustrated) of the controlcircuit 500.

FIGS. 8A and 8B are diagrams schematically showing modifications of theoptical scan device 100 shown in FIG. 7.

In the example shown in FIG. 8A, each of the plurality of phase shifters80 is spatially divided into a first phase shifter section 80φ and asecond phase shifter section 80V. The first phase shifter section 80φand the second phase shifter section 80V are connected in series. Thesecond phase shifter section 80V is connected to a corresponding one ofthe optical waveguides 10. The arrangement of the first phase shiftersection 80φ and the second phase shifter section 80V may be inverted.

In the example shown in FIG. 8B, the first phase shifters 80φ of thephase shifters 80 are arranged in a cascade within the optical divider90. The second phase shifters 80V are connected in series to eachseparate optical waveguide 10.

In each of the examples shown in FIGS. 8A and 8B, the control circuit500 controls the first shift amount φ_(i) of the first phase shifter 80φand controls the second shift amount V_(i) of the second phase shiftersection 80V. As a result, as in the case of the example shown in FIG. 7,light obtained by shifting, by (i−1)Δφ+V_(i), the phase of lightinputted to the optical divider 90 is inputted to the ith opticalwaveguide 10 as counted from the bottom.

Next, another example of control of the second shift amount V_(i) isdescribed.

FIG. 9 is a diagram schematically showing an example of the optical scandevice 100 according to the present embodiment and an example of thedirection of the light beam that is emitted from the optical waveguidearray 10A. In the example shown in FIG. 9, the plurality of phaseshifters 80 includes two phase shifter groups 80 g. A first one of thephase shifter groups 80 g includes lower four phase shifters, and asecond one of the phase shifter groups 80 g includes upper four phaseshifters. As mentioned above, the control circuit 500 determines thefirst shift amount φ_(i) in accordance with the first control signal 500a. The control circuit 500 sets second phase shift amounts V₁ to V₄ toV_(a) in the first phase shifter group 80 g and sets second phase shiftamounts V₅ to V₈ to V_(b) in the second phase shifter group 80 g inaccordance with the second control signal 500 b. V_(a) and V_(b) aredifferent. Light emitted from the lower four optical waveguides 10 viathe first phase shifter group 80 g interferes with light emitted fromthe upper four optical waveguides 10 via the second phase shifter group80. As a result, a light beam outputted from the optical waveguide array10A splits into two light beams.

Phase shift amounts of light within each separate phase shifter group 80g vary by Δφ in the order in which the phase shifters are arrayed.Meanwhile, with a focus shifted from one phase shifter group 80 g toanother adjacent phase shifter group 80 g, phase shift amounts of lightvary by an amount that is different from Δφ. In the example shown inFIG. 9, the amount that is different from Δφ is Δφ+V_(b)−V_(a). In otherwords, the phase shift amount Δφ+V_(b)−V_(a) between two phase shiftersat a boundary between adjacent phase shifter groups is different fromthe phase shift amount Δφ between two adjacent phase shifters in onephase shifter group.

In summary, the plurality of phase shifters 80 are constituted by aplurality of phase shifter groups 80 g arranged in the Y direction. Eachof the plurality of phase shifter groups includes one or more phaseshifters 80. The control circuit 500 determines the second shift amountV_(i) so that it varies from one phase shifter group 80 g to another.

FIGS. 10A to 10C are diagrams schematically showing modifications of theoptical scan device 100 shown in FIG. 9.

In the example shown in FIG. 10A, the phase shifter array 80A isspatially divided into eight first phase shifter sections 80φ and foursecond phase shifter sections 80V. In the optical divider 90, one ormore branch points are present between a first phase shifter section 80φand a second phase shifter section 80V. In the example shown in FIG.10A, the control circuit 500 sets second phase shift amounts to V_(a) inlower two second phase shifter sections 80V and sets second phase shiftamounts to V_(b) in upper two second phase shifter sections 80V. As aresult, the phase of light that is inputted to the optical waveguidearray 10A is the same as it is in the example shown in FIG. 9.

In the example shown in FIG. 10B, the phase shifter array 80A isspatially divided into eight first phase shifter sections 80φ and twosecond phase shifter sections 80V. The arrangement of the eight firstphase shifter sections 80φ and the two second phase shifter sections 80Vmay be inverted. A lower common second phase shifter section 80V isconnected to lower four first phase shifter sections 80φ. An uppercommon second phase shifter section 80V is connected to upper four firstphase shifter sections 80φ. In the example shown in FIG. 10A, thecontrol circuit 500 sets second phase shift amounts to V_(a) in lowertwo second phase shifter sections 80V and sets second phase shiftamounts to V_(b) in upper two second phase shifter sections 80V. As aresult, the phase of light that is inputted to the optical waveguidearray 10A is the same as it is in the example shown in FIG. 9.

In the example shown in FIG. 10C, the plurality of phase shifters 80 arearranged in a cascade within the optical divider 90. The control circuit500 sets the phase shift amount of the lowermost phase shifter 80 toV_(a), sets the phase shifter amount of the fifth phase shifter 80 ascounted from the bottom to Δφ+V_(b)−V_(a), and sets the phase shiftamounts of the other phase shifters 80 to Δφ. As a result, the phase oflight that is inputted to the optical waveguide array 10A is the same asit is in the example shown in FIG. 9.

Next, a relationship between the first and second shift amounts φ_(i)and V_(i) and the shape of a light beam in a far field is described withreference to the example shown in FIG. 7.

In the example shown in FIG. 7, the center of the lowermost opticalwaveguide 10 is located at the origin. In a case where r is the distancebetween the origin and a place in a far field, the distance n betweenthe center of the ith optical waveguide 10 as counted from the bottomand the place in the far field is approximated as n≈r−(i−1)(p·sin α₀).As shown in FIG. 3B, p is an array cycle of optical waveguides 10 and α₀is an angle of emission of light. (i−1)(p·sin α₀) is a distance obtainedby orthogonally projecting the distance (i−1)p between the origin andthe center of the ith optical waveguide 10 onto a line of the distance rconnecting the origin with the place in the far field. That is, n isapproximated by subtracting the orthogonally projected distance(i−1)(p·sin α₀) from the distance r between the origin and the place inthe far field.

For this reason, in a case where Δφ(i−1)+V_(i) is added to the phase oflight that is inputted to the ith optical waveguide 10 as counted fromthe bottom, an electric field of light that is emitted from the ithoptical waveguide 10 as counted from the bottom is expressed by Formula(4) in the far field as follows:

$\begin{matrix}{E_{i} = {{\left( \frac{\sin\; b}{b} \right)e^{- {j{\lbrack{{kr}_{i} + {{\Delta\phi}{({i - 1})}} + V_{i}}\rbrack}}}}\overset{.}{\underset{.}{=}}{\left( \frac{\sin\; b}{b} \right)e^{- {j{\lbrack{{kr} - {{({{2a} - {\Delta\phi}})}{({i - 1})}} + V_{i}}\rbrack}}}}}} & (4)\end{matrix}$

where

$\begin{matrix}{a = {\frac{2\;\pi}{\lambda}\frac{p}{2}\sin\;\alpha_{0}}} & (5) \\{b = {\frac{2\;\pi}{\lambda}\frac{w}{2}\sin\;\alpha_{0}}} & (6)\end{matrix}$

k is a wave number 2π/λ, and w is the width of the optical waveguide 10in the Y direction. The electric field in the far field is equivalent tothe total of electric fields of light emitted from an array number N ofoptical waveguides 10. Accordingly, the electric field in the far-fieldis expressed by Formula (7) as follows:

$\begin{matrix}{E_{total} = {{\sum\limits_{i = 1}^{N}E_{i}} = {\left( \frac{\sin\; b}{b} \right)e^{- {jkr}}{\sum\limits_{i = 1}^{N}e^{j{\lbrack{{{({{2\; a} - {\Delta\phi}})}{({i - 1})}} - V_{i}}\rbrack}}}}}} & (7)\end{matrix}$

A light intensity distribution in the far filed is obtained by thesquare of the absolute value of E_(total). Accordingly, the lightintensity distribution I(α₀) in the far field is expressed by Formula(8) as follows:

$\begin{matrix}{{I\left( \alpha_{0} \right)} = {{E_{total}}^{2} = {\left( \frac{\sin\; b}{b} \right)^{2}{{\sum\limits_{i = 1}^{N}e^{j{\lbrack{{{({{2\; a} - {\Delta\phi}})}{({i - 1})}} - V_{i}}\rbrack}}}}^{2}}}} & (8)\end{matrix}$

When V_(i)=0, the light intensity distribution I(α₀) is expressed byFormula (9) as follows:

$\begin{matrix}{{I\left( \alpha_{0} \right)} = {\left( \frac{\sin\; b}{b} \right)^{2}{\frac{\sin\;{N\left( {a - {{\Delta\phi}\text{/}2}} \right)}}{\sin\;\left( {a - {{\Delta\phi}\text{/}2}} \right)}}^{2}}} & (9)\end{matrix}$

The light intensity distribution I(α₀) reaches its maximum when a=Δφ/2.This is the same condition as Formula (2), which has been mentionedbefore.

FIG. 11 is a diagram showing a relationship between the angle α₀ and thelight intensity distribution I(α₀) when the second shift amount V_(i) iszero. Wavelength λ=1.55 μm, Array Cycle p=3 μm, Optical Waveguide Widthw=1 μm, and N=32. The solid line, the dotted line, and the dashed linerepresent results obtained by determining Δφ at the first shift amountφ_(i) so that α₀=0°, α₀=10°, and α₀=20°, respectively. As shown in FIG.11, the light intensity distribution I(α₀) indicates a peak at each ofα₀=0°, α₀=10°, and α₀=20°. The width of a peak shown in FIG. 11 isequivalent to the spread angle of a light beam.

FIGS. 12A and 12B are diagrams each showing a relationship between theangle α₀ and the light intensity distribution I(α₀) when the secondshift amount V_(i) is not zero. Conditions are the same as those of theexample shown in FIG. 11, except for the second shift amount V_(i). Ineach of the examples shown in FIGS. 12A and 12B, a phase shifter array80A whose array number N is equal to 32 includes two phase shiftergroups 80 g. Each of the two phase shifter groups 80 g includes an arraynumber N/2=16 of phase shifters 80.

In the example shown in FIG. 12A, the second shift amount V_(i) is equalto 0.05π in a first one of the two phase shifter groups 80 g, and thesecond shift amount V_(i) is equal to −0.05π in a second one of the twophase shifter groups 80 g. As shown in FIG. 12A, the light intensitydistribution I(α₀) indicates a peak at each of α₀=0°, α₀=10°, andα₀=20°. The width of a peak shown in FIG. 12A is wider than the width ofa peak shown in FIG. 11. Meanwhile, the central angle of a peak shown inFIG. 12A is substantially the same as the central angle of a peak shownin FIG. 11.

In the example shown in FIG. 12B, the second shift amount V_(i) is equalto 0.1π in a first one of the two phase shifter groups 80 g, and thesecond shift amount V_(i) is equal to −0.1π in a second one of the twophase shifter groups 80 g. As shown in FIG. 12B, the light intensitydistribution I(α₀) indicates a peak at each of α₀=0°, α₀=10°, andα₀=20°. The peak includes two subpeaks into which it splits, as thephase difference between the two phase shifter groups 80 g is great. Inthis example, the width of the peak is a total of the widths of the twosubpeaks. The width of a peak shown in FIG. 12B is wider than the widthof a peak shown in FIG. 12A. Meanwhile, the central angle of a peakshown in FIG. 12B is substantially the same as the central angle of apeak shown in FIG. 12A.

Results shown in FIGS. 12A and 12B show that the direction of a lightbeam is determined by the first shift amount φ_(i) and the spread angleof a light beam is determined by the second shift amount V_(i). In thisway, by adjusting the second shift amount Vi of each phase shifter 80,the control circuit 500 allows the optical waveguide array 10A to emit alight beam having a predetermined spread angle.

FIG. 13 is a diagram showing a relationship between the angle α₀ and thelight intensity distribution I(α₀) when the second shift amount V_(i) isnot zero and Δφ at the first shift amount φ_(i) is determined so thatα₀=10°. In the example shown in FIG. 13, a phase shifter array 80A whosearray number N is equal to 64 includes eight phase shifter groups 80 g.Each of the eight phase shifter groups 80 g includes an array numberN/8=8 of phase shifters 80. In the eight phase shifter groups 80 g, thesecond phase shift amounts V_(i) are equal to −0.09π, 0.12π, 0.06π, 0π,0.03π, −0.1π, 0.06π, 0.09π, respectively. As shown in FIG. 13, the lightintensity distribution I(α₀) indicates a peak at α₀=10°. Unlike in theexample shown in FIG. 12B, the peak does not split into two subpeaks. Inthis way, by setting discrete second shift amounts V_(i) for eachseparate phase shifter group 80 g, the peak can be spread without beingsplit. The second shift amounts V_(i) that are determined for eachseparate phase shifter group 80 g may be determined, for example, on thebasis of random numbers. This makes it possible to curb the influence ofinterference of light between phase shifter groups 80 g. This in turnmakes it hard for a peak to appear, attaining an uniform intensitydistribution of a light beam.

As stated above, the control circuit 500 can independently change afirst control parameter that controls the direction of the light beamand a second control parameter that controls the shape of the lightbeam. In each of the examples shown in FIGS. 6A and 6B, the firstcontrol parameter is the phase shift amount (pi, and the second controlparameter is equivalent of the switching of light input by the opticalswitch. In each of the examples shown in FIG. 7, FIG. 9, and FIGS. 10Aand 10B, the first control parameter is the first shift amount φ_(i),and the second control parameter is the second shift amount V_(i).

In each of the examples shown in FIGS. 6A to 13, the optical waveguides10 are not limited to reflective optical waveguides. For example, theoptical waveguides 10 may be optical waveguides through which lightpropagates by total reflection. In a case where such optical waveguidesare used as the optical waveguides 10, light is emitted in a directionparallel to the XY plane not from an upper surface of the opticalwaveguide array 10A but from an end of the optical waveguide array 10Ain FIGS. 6A and 6B, FIG. 7, FIG. 9, and FIGS. 10A and 10B.

The aforementioned examples have described the control of a Y-directioncomponent of the direction of a light beam emitted from the optical scandevice 100 and the shape of the light beam in the Y direction. Thefollowing describes the control of an X-direction component of thedirection of a light beam emitted from the optical scan device 100 andthe shape of the light beam in the X direction.

FIG. 14A is a diagram schematically showing an optical waveguide 10according to the present embodiment. The optical waveguide 10 includes afirst mirror 30, a second mirror 40, an optical waveguide 20, and a pairof electrodes 62 a and 62 b. The first mirror 30 extends in the Xdirection. The second mirror 40 faces the first mirror 30 and extends inthe X direction. The optical waveguide layer 20 is located between thefirst mirror 30 and the second mirror 40, and propagates light along theX direction. The transmittance of the first mirror 30 is higher than thetransmittance of the second mirror 40. Light that is emitted via thefirst mirror 30 from the optical waveguide layer 20 of each of aplurality of the optical waveguides 10 interferes. This causes a lightbeam to be emitted from the optical waveguide array 10A.

In the example shown in FIG. 14A, the optical waveguide layer 20 isconstituted by a material whose refractive index changes when a voltageis applied. The optical waveguide layer 20 contains for example a liquidcrystal material or an electro-optical material. The pair of electrodes62 a and 62 b directly or indirectly holds the optical waveguide layer20 therebetween. As shown in FIG. 14A, the first mirror 30 may belocated between the optical waveguide layer 20 and the upper electrode62 b, and the second mirror 40 may be located between the opticalwaveguide layer 20 and the lower electrode 62 a. In the example shown inFIG. 14A, the lower electrode 62 a is a pattern electrode including aplurality of electrode sections arranged in the X direction. Instead ofthe lower electrode 62 a, the upper electrode 62 b may be a patternelectrode. Alternatively, in addition to the lower electrode 62 a, theupper electrode 62 b may be a pattern electrode.

By controlling voltages that are applied between the plurality ofelectrode sections of the lower electrode 62 a and the upper electrode62, the control circuit 500 can adjust the refractive indices ofportions of the optical waveguide layer 20 that overlap the plurality ofelectrode sections when seen from the Z direction. This allows lights tobe emitted via the first mirror 30 in different directions from theportions of the optical waveguide layer 20 that overlap the plurality ofelectrode sections. This in turn makes it possible to change aX-direction component of the direction of the light beam that is emittedfrom the optical waveguide array 10A and the shape of the light beam inthe X direction. The portions of the optical waveguide layer 20 thatoverlap the plurality of electrode sections when seen from the Zdirection are hereinafter referred to simply as “portions overlappingthe plurality of electrode sections”.

In the example shown in FIG. 14A, the lower electrode 62 a is a patternelectrode including five electrode sections. The application of voltagesto the five electrode sections changes the refractive indices n_(w1) ton_(w5) of the portions overlapping the plurality of electrode sections.This also changes the angles of emission θ₁ to θ₅ of lights that areemitted via the first mirror 30 from the portions overlapping theplurality of electrode sections.

FIG. 14B is a diagram showing a relationship between the refractiveindex n_(w) of the optical waveguide layer 20 and the angle of emissionof light that is emitted from the optical waveguide 10. In Formula (1),d=0.62 μm, λ=1.55 μm, and m=1 are used. As shown in FIG. 14B, a changefrom Refractive Index n_(w)=1.5 by −0.0355 causes the angle of emissionθ to decrease by −6.3 degrees.

The control circuit 500 may control the direction of the light beam inaccordance with a third control signal 500 c and control the shape ofthe light beam in accordance with a fourth control signal 500 d. Thedirection of the light beam is determined, for example, by the averageof the angles of emission of lights that are emitted from the portionsoverlapping the plurality of electrode sections. The shape of the lightbeam is determined, for example, by the difference between the maximumand minimum values of the angles of emission of lights that are emittedfrom the portions overlapping the plurality of electrode sections.

In a case where the lower electrode 62 a includes M electrode sections,the angles of emission of lights that are emitted via the first mirror30 from the portions overlapping the plurality of electrode sections arerepresented as θ₁ to θ_(M), respectively. In a case where θ is thedirection of emission of the light beam and Δθ is the spread angle, therefractive index n_(wj) of a portion overlapping the jth electrodesection of the M electrode sections in the X direction is adjusted, forexample, so that θ_(j)=θ−(Δθ/2)+Δθ[(j−1)/(M−1)]. In this case, themaximum value of the angles of emission is given as θ_(M)=θ+Δθ/2, andthe minimum value is given as θ₁=θ−Δθ/2. This is not the onlycombination of θ₁ to θ_(M). With the spread angle being Δθ, anycombination of θ₁ to θ_(M) is possible. θ₁ to θ_(M) may be set, forexample, on the basis of random numbers. For example, the spread angleof a spot of emitted light is given as Δθ=6.3°, provided the refractiveindices of the plurality of portions of the optical waveguide layer 20fall within a range of n_(w1)=1.4645 to n_(wM)=1.50.

From Formula (1), the refractive index n_(w)=n₀ that satisfies thedesired angle of emission θ of the light beam is determined. The voltagethat is applied to each of the plurality of electrode sections is thesum of a first voltage and a second voltage. The control circuit 500applies such a first voltage to each of the plurality of electrodesections in accordance with the third control signal 500 c that therefractive indices of the portions overlapping the plurality ofelectrode sections become no. The control circuit 500 applies suchsecond voltages to the plurality of electrode sections, respectively, inaccordance with the fourth control signal 500 d that the refractiveindices of the portions overlapping the plurality of electrode sectionsare corrected to become n₀ to n_(wj). In this way, the control circuit500 controls the direction of the light beam by controlling the firstvoltage and controls the shape of the light beam by controlling thesecond voltage. For the same reasons as those mentioned above,independently controlling the direction and shape of a light beam inaccordance with two control signals makes it possible to greatly reducethe number of data that represent control signals that are stored in thememory (not illustrated) of the control circuit 500.

As stated above, the optical scan device 100 according to the presentembodiment makes it possible to arbitrarily change X-direction andY-direction components of the direction of the light beam and the shapesof the light beam in the X direction and the Y direction.

FIGS. 15A to 15C are diagrams each schematically showing an example ofthe shape of a light beam 305 that is emitted from the optical waveguidearray 10A of the optical scan device 100. In each of the examples shownin FIGS. 15A to 15C, the optical scan device 100 and a photodetector 400are disposed on a substrate. The photodetector 400 is for example animage sensor. Light emitted from the optical waveguide array 10A andreflected off and returning from a physical object is detected by thephotodetector 400.

In the example shown in FIG. 15A, the light beam 305 is a diffused beam.The diffused beam has such a spread angle that a target area is coveredwith one beam. This makes it possible to irradiate a wide range withoutpassing the light beam over it. Meanwhile, the diffused beam has acomparatively short range. For this reason, the diffused beam is used tomeasure an object at a comparatively short distance.

In the example shown in FIG. 15B, the light beam 305 is a line beam(which is an example of a line scan beam of the present disclosure). Thespread angle of the line beam in the Y direction is larger than thespread angle of the line beam in the X direction. While the line beamhas such a spread angle that a range of a target area in the Y directionis covered with one beam, a range of the target area in the X directioncannot be covered with one beam. Accordingly, the light beam is passedin the X direction. The relationship in magnitude between the spreadangles of the line beam in the X direction and the Y direction may beinverted. Unlike the diffused beam, the line beam is passed in aone-dimensional direction. Meanwhile, the line beam has a longer rangethan the diffused beam. This makes it possible to measure a physicalobject at a longer distance. In the case of the line beam, the controlcircuit 500 controls the direction of the light beam so that the lightbeam is passed in one of the X and Y directions that is smaller inspread angle.

In the example shown in FIG. 15C, the light beam 305 is a spot beam(which is an example of a two-dimensional scan beam of the presentdisclosure). The spot beam cannot cover ranges of a target area in boththe X direction and the Y direction with one beam. For this reason, thelight beam is passed in both the X direction and the Y direction. Unlikethe line beam, the spot beam is passed in a two-dimensional direction.Meanwhile, the spot beam has a further longer range than the line beam.This makes it possible to measure a physical object at a further longerdistance.

The optical scan device 100 may irradiate, with a light beam having afirst spread angle, a first area in a scene that the photodetector 400shoots and irradiate, with a light beam having a second spread anglethat is larger than the first spread angle, a second area in the scenethat is located at a shorter distance than the first area. By thusarbitrarily changing the shape of the light beam 305, distances tophysical objects at a short distance and a long distance can beaccurately measured.

The optical scan device 100 according to the present embodiment alsobrings about the following effects.

Conventionally, there has been known a method for measuring a distanceto a physical object by emitting lights in different directions from aplurality of light sources and detecting, through an image sensor, lightreflected off and returning from the physical object. This methodirradiates a physical object with lights emitted in different directionsfrom the plurality of light sources. This causes parallax differencesthat lead to differences in location of the shadow of the physicalobject to be detected. As a result, it is not easy to reconstruct onedistance image by integrating distance images of the physical object asacquired from the plurality of light sources, respectively.

Meanwhile, the optical scan device 100 according to the presentembodiment is configured such that a light beam of a given shape isemitted in a given direction from one device. Accordingly, there are noparallax differences.

FIG. 16 is a diagram schematically showing examples of light beams 305that are emitted from the optical scan device 100 according to thepresent embodiment and examples of distance images.

The first, second, and third left drawings of FIG. 16 as counted fromthe top represent light beams 305, emitted from the optical scan device100, that have a large beam spot 310, a medium beam spot 310, and asmall beam spot 310, respectively.

The first, second, and third right drawings of FIG. 16 as counted fromthe top represent distance images obtained by the large beam spot 310,the medium beam spot 310, and the small beam spot 310, respectively. Thelowermost right drawing of FIG. 16 represents a distance image intowhich the three distance images have been integrated.

As shown in FIG. 16, the optical scan device 100 acquires a plurality ofdistance images of physical objects at a short distance, a middledistance, and a long distance through a plurality of light beams ofdifferent directions and shapes. As shown in the lowermost right drawingof FIG. 16, a distance image of physical objects can be easilyreconstructed by adding up and integrating the plurality of distanceimages into one distance image.

Examples of Application

FIG. 17 is a diagram showing an example configuration of an optical scandevice 100 in which elements such as an optical divider 90, an opticalwaveguide array 10A, a phase shifter array 80A, and a light source 130are integrated on a circuit board (e.g. a chip). The light source 130may for example be a light-emitting element such as a semiconductorlaser. In this example, the light source 130 emits single-wavelengthlight whose wavelength in free space is λ. The optical divider 90divides the light from the light source 130 into lights and introducesthe lights into optical waveguides of the plurality of phase shifters80. In the example shown in FIG. 17, there are provided an electrode 62Aand a plurality of electrodes 62B on the chip. The optical waveguidearray 10A is supplied with a control signal from the electrode 62A. Tothe plurality of phase shifters 80 in the phase shifter array 80A,control signals are sent from the plurality of electrodes 62B,respectively. The electrode 62A and the plurality of electrodes 62B maybe connected to a control circuit (not illustrated) that generates thecontrol signals. The control circuit may be provided on the chip shownin FIG. 17 or may be provided on another chip in the optical scan device100.

As shown in FIG. 17, an optical scan over a wide range can be achievedthrough a small-sized device by integrating all components on the chip.For example, all of the components shown in FIG. 17 can be integrated ona chip measuring approximately 2 mm by 1 mm.

FIG. 18 is a schematic view showing how a two-dimensional scan is beingexecuted by irradiating a distant place with a light beam such as alaser from the optical scan device 100. A two-dimensional can isexecuted by moving a beam spot 310 in horizontal and verticaldirections. For example, a two-dimensional ranging image can be acquiredby a combination with a publicly-known TOF method. The TOF method is amethod for, by observing light reflected from a physical objectirradiated with a laser, calculating the time of fight of the light tofigure out the distance.

FIG. 19 is a block diagram showing an example configuration of a LiDARsystem 300 serving as an example of a photodetection system that iscapable of generating such a ranging image. The LiDAR system 300includes an optical scan device 100, a photodetector 400, a signalprocessing circuit 600, and a control circuit 500. The photodetector 400detects light emitted from the optical scan device 100 and reflectedfrom a physical object. The photodetector 400 may for example be animage sensor that has sensitivity to the wavelength λ of light that isemitted from the optical scan device 100 or a photodetector including aphoto-sensitive element such as a photodiode. The photodetector 400outputs an electrical signal corresponding to the amount of lightreceived. The signal processing circuit 600 calculates the distance tothe physical object on the basis of the electrical signal outputted fromthe photodetector 400 and generates distance distribution data. Thedistance distribution data is data that represents a two-dimensionaldistribution of distance (i.e. a ranging image). The control circuit 500is a processor that controls the optical scan device 100, thephotodetector 400, and the signal processing circuit 600. The controlcircuit 500 controls the timing of irradiation with a light beam fromthe optical scan device 100 and the timing of exposure and signalreadout of the photodetector 400 and instructs the signal processingcircuit 600 to generate a ranging image.

The frame rate at which a ranging image is acquired by a two-dimensionalscan can be selected, for example, from among 60 fps, 50 fps, 30 fps, 25fps, 24 fps, or other frame rates, which are commonly used to acquiremoving images. Further, in view of application to an onboard system, ahigher frame rate leads to a higher frequency of acquisition of aranging image, making it possible to accurately detect an obstacle. Forexample, in the case of a vehicle traveling at 60 km/h, a frame rate of60 fps makes it possible to acquire an image each time the vehicle movesapproximately 28 cm. A frame rate of 120 fps makes it possible toacquire an image each time the vehicle moves approximately 14 cm. Aframe rate of 180 fps makes it possible to acquire an image each timethe vehicle moves approximately 9.3 cm.

The time required to acquire one ranging image depends on the speed of abeam scan. For example, in order for an image whose number of resolvablespots is 100 by 100 to be acquired at 60 fps, it is necessary to performa beam scan at 1.67 μs or less per point. In this case, the controlcircuit 500 controls the emission of a light beam by the optical scandevice 100 and the storage and readout of a signal by the photodetector400 at an operating speed of 600 kHz.

Example of Application to Optical Receiver Device

Each of the optical scan devices according to the aforementionedembodiments of the present disclosure can also be used as an opticalreceiver device of similar configuration. The optical receiver deviceincludes an optical waveguide array 10A which is identical to that ofthe optical scan device and a first adjusting element that adjusts thedirection of light that can be received. Each of the first mirrors 30 ofthe optical waveguide array 10A transmits light falling on a sidethereof opposite to a first specular surface from the third direction.Each of the optical waveguide layers 20 of the optical waveguide array10A causes the light transmitted through the first mirror 30 topropagate in the second direction. The direction of light that can bereceived can be changed by the first adjusting element changing at leastone of the refractive index of the optical waveguide layer 20 of eachoptical waveguide element 10, the thickness of the optical waveguidelayer 20 of each optical waveguide element 10, or the wavelength oflight. Furthermore, in a case where the optical receiver device includesa plurality of phase shifters 80 or 80 a and 80 b which are identical tothose of the optical scan device and a second adjusting element thatvaries differences in phase among lights that are outputted through theplurality of phase shifters 80 or 80 a and 80 b from the plurality ofoptical waveguide elements 10, the direction of light that can bereceived can be two-dimensionally changed.

For example, an optical receiver device can be configured such that thelight source 130 of the optical scan device 100 shown in FIG. 17 issubstituted by a receiving circuit. When light of wavelength λ falls onthe optical waveguide array 10A, the light is sent to the opticaldivider 90 through the phase shifter array 80A, is finally concentratedon one place, and is sent to the receiving circuit. The intensity of thelight concentrated on that one place can be said to express thesensitivity of the optical receiver device. The sensitivity of theoptical receiver device can be adjusted by adjusting elementsincorporated separately into the optical waveguide array 10A and thephase shifter array 80A. The optical receiver device is opposite indirection of the wave number vector (in the drawing, the bold arrow)shown, for example, in FIG. 4. Incident light has a light componentacting in the direction (in the drawing, the X direction) in which theoptical waveguide elements 10 extend and a light component acting in thearray direction (in the drawing, the Y direction) of the opticalwaveguide elements 10. The sensitivity to the light component acting inthe X direction can be adjusted by the adjusting element incorporatedinto the optical waveguide array 10A. Meanwhile, the sensitivity to thelight component acting in the array direction of the optical waveguideelements 10 can be adjusted by the adjusting element incorporated intothe phase shifter array 80A. θ and α₀ shown in FIG. 4 are found from thephase difference Δφ of light and the refractive index n_(w) andthickness d of the optical waveguide layer 20 at which the sensitivityof the optical receiver device reaches its maximum. This makes itpossible to identify the direction of incidence of light.

The aforementioned embodiments may be combined as appropriate.

An optical scan device and an optical receiver device according to anembodiment of the present disclosure are applicable, for example, to ause such as a LiDAR system that is mounted on a vehicle such as anautomobile, a UAV, or an AGV.

What is claimed is:
 1. A photodetection system comprising: an opticalwaveguide array, including a plurality of optical waveguides each ofwhich propagates light along a first direction, that emits a light beam,the plurality of optical waveguides being arranged in a second directionthat intersects the first direction; a phase shifter array including aplurality of phase shifters connected separately to each of theplurality of optical waveguides; a control circuit that controls a phaseshift amount of each of the plurality of phase shifters and/or inputtingof light to each of the plurality of phase shifters and thereby controlsa direction and shape of the light beam that is emitted from the opticalwaveguide array; a photodetector that detects the light beam reflectedby a physical object; and a signal processing circuit that generatesdistance distribution data on the basis of output from thephotodetector.
 2. The photodetection system according to claim 1,wherein the control circuit is capable of independently changing a firstcontrol parameter that controls the direction of the light beam and asecond control parameter that controls the shape of the light beam. 3.The photodetection system according to claim 2, wherein the phase shiftamount of each of the plurality of phase shifters is a sum of a firstshift amount and a second shift amount, and the control circuit controlsthe direction of the light beam by controlling the first control shiftamount of each of the plurality of phase shifters and controls the shapeof the light beam by controlling the second shift amount of each of theplurality of phase shifters.
 4. The photodetection system according toclaim 3, wherein the second direction is perpendicular to the firstdirection, the plurality of optical waveguides are arranged at equalspacings in the second direction, the plurality of phase shifters arearranged as equal spacings in the second direction and connecteddirectly to the plurality of optical waveguides, and the control circuitdetermines the first shift amount of each of the plurality of phaseshifters so that the first shift amount varies by a constant amount inan order in which the plurality of phase shifters are arrayed in thesecond direction.
 5. The photodetection system according to claim 3,wherein the control circuit adjusts the second shift amount of each ofthe plurality of phase shifters and thereby causes the optical waveguidearray to emit a light beam having a predetermined spread angle.
 6. Thephotodetection system according to claim 5, wherein the control circuitdetermines the second shift amount of each of the plurality of phaseshifters on the basis of random numbers.
 7. The photodetection systemaccording to claim 1, wherein the plurality of phase shifters areconstituted by a plurality of phase shifter groups arranged in thesecond direction, each of the plurality of phase shifter groups includesone or more phase shifters, and a difference in phase shift amountbetween two phase shifters at a boundary between adjacent phase shiftergroups is different from a difference in phase shift amount between twoadjacent phase shifters in one phase shifter group.
 8. Thephotodetection system according to claim 2, wherein the control circuitcontrols the direction of the light beam by controlling the phase shiftamount of each of the plurality of phase shifters and controls the shapeof the light beam by controlling the inputting of the light to each ofthe plurality of phase shifters.
 9. The photodetection system accordingto claim 1, wherein each of the plurality of phase shifters includes anoptical waveguide connected to a corresponding one of the plurality ofwaveguides, the optical waveguide is constituted by a material whoserefractive index changes when a voltage is applied, and the controlcircuit changes the phase shift amount by changing the refractive indexby applying the voltage to the optical waveguide of each of theplurality of phase shifters.
 10. The photodetection system according toclaim 9, further comprising a pair of electrodes directly or indirectlyholding the optical waveguide of each of the plurality of phase shifterstherebetween, wherein the optical waveguide of each of the plurality ofphase shifters contains a liquid crystal material or an electro-opticalmaterial, and the control circuit changes the refractive index of theoptical waveguide by applying the voltage to the pair of electrodes. 11.The photodetection system according to claim 1, wherein each of theplurality of optical waveguides includes a first mirror extending in thefirst direction, a second mirror facing the first mirror and extendingin the first direction, and an optical waveguide layer, located betweenthe first mirror and the second mirror, that propagates light along thefirst direction, a transmittance of the first mirror is higher than atransmittance of the second mirror, and the light beam is emitted viathe first mirror from the plurality of optical waveguides.
 12. Thephotodetection system according to claim 11, further comprising firstand second electrodes directly or indirectly holding the opticalwaveguide layer therebetween, wherein the optical waveguide layer ofeach of the plurality of optical waveguides is constituted by a materialwhose refractive index changes when a voltage is applied, the firstelectrode includes a plurality of electrode sections arranged in thefirst direction, and the control circuit controls voltages that areapplied between the plurality of electrode sections of the firstelectrode and the second electrode and thereby changes the direction andshape of the light beam that is emitted from the optical waveguidearray.
 13. The photodetection system according to claim 12, wherein thevoltages that are applied to the plurality of electrode sections areeach a sum of a first voltage and a second voltage, and the controlcircuit controls the direction of the light beam by controlling thefirst voltage and controls the shape of the light beam by controllingthe second voltage.
 14. The photodetection system according to claim 12,wherein the material whose refractive index changes when a voltage isapplied is a liquid crystal material or an electro-optical material. 15.The photodetection system according to claim 11, wherein a spread anglein either one of the first or second directions of the light beam thatis emitted from the optical waveguide array is larger than a spreadangle in the other one of the first or second directions of the lightbeam that is emitted from the optical waveguide array, and the controlcircuit controls the direction of the light beam so that the light beamis passed in one of the first and second directions that is smaller inspread angle.
 16. A photodetection system comprising: an optical scandevice that is capable of controlling a direction and shape of a lightbeam; an image sensor, having a plurality of pixels, that detects thelight beams reflected by a scene; a control circuit that controls thedirection and shape of the light beam that is emitted from the opticalscan device; and a signal processing circuit that generates distancedistribution data on the basis of output from the image sensor, whereinthe control circuit causes the optical scan device to emit a pluralityof light beams differing in direction of emission and spread angle fromeach other, and the image sensor detects the plurality of light beamsreflected by the scene.
 17. The photodetection system according to claim16, wherein the optical scan device irradiates, with the light beamhaving a first spread angle, a first area in the scene that the imagesensor shoots and irradiates, with the light beam having a second spreadangle that is larger than the first spread angle, a second area in thescene that is at a shorter distance than the first area.
 18. Thephotodetection system according to claim 16, wherein the signalprocessing circuit integrates the distance distribution data obtained bythe image sensor detecting the plurality of light beams.
 19. Thephotodetection system according to claim 16, wherein the plurality oflight beams include a diffused beam and a line scan beam.
 20. Thephotodetection system according to claim 16, wherein the plurality oflight beams include a diffused beam and a two-dimensional scan beam. 21.The photodetection system according to claim 16, wherein the pluralityof light beams include a line scan beam and a two-dimensional scan beam.